Process of metal recovery



Patented Sept. 24, 1946' PROCESS OEMETAL mioov aY; Philip '1. Stroup andCharles 'B; 'Wil1more, New "1 .Kensington, Pa., assignors-to AluminumCom-1 pany of America, Pittsburgh, Pa., a corporation:

of Pennsylvania 7N0 Drawing. Application March so, 1945.

Serial'No. 585,816 6Claims. (or; 75-67) This invention relates to thoseprocesses of metal recovery in which a gas-vapor mixture containingcarbonmonoxide and a vapor or a metal miscible with molten aluminum ispassed into contact with a body of molten aluminum for the purpose ofcondensing and absorbing the metal of the gaseous mixture and therebyeffecting separation between the metal vapor andthe carbon monoxide andother non-metallic components of the gas-vapor mixture. v

Such a process is particularly useful when it is desired to obtainmetals, uch as zinc '01 magnesium, directly. from their 'oxidic'ores byheating said ores with carbon ofabarbonaceous substance at temperaturesin excess of the boiling point of the metal to be recovered. In suchcases the process tends to be reversible and if immediate and completeseparation'is not achieved be-' tween the gaseous products of reaction,which include the metal vapor and the carbon monoxide, the CO will reactwith the zinc or magnesium vapor to again form the oxide of the metaland thus prevent the desired recovery of the metal. Molten aluminum is avaluable medium for effecting the. desired separation, not only becauseof its miscibility with zinc or magnesium, but also because it formswith'either of those metals a .useful series of commercial alloys andit'is thus possi=b1e .to produce directly by, the separation orabsorption process a usable. product which, if desired, may beutilizediwithout further processing by distillation or'other familiarstep, to separate the dissolved metal from the aluminum.-

Whenever a body of molten aluminum is used as amedium by which ametallic vapor, is condensed and separated from a gas-vapor mixturewhich contains the monoxideof carbon'there is formed, as a result ofcontact between the alumi num body and the carbon monoxide, asludge ordross which causes serious mechanical handling difficulties and alsotends to contaminate the alloy which is the product of theoperations.This sludge or dross contains metal carbides, metal oxides and carbon.It is usually of great volume in relation to its weight and, if notcontrolled, may form with such rapidity and in such volume as tomechanically impede and clog the vessel or chamber in which contactbetween the gas-vapor mixture and the molten aluminum body isestablished. V 1

It is the object of this invention to eliminate, or substantiallyimpede, the formation of this S u e or dross during the above describedoperation and we have found that the presence in the molten aluminumbody of certain metals in relav 2 tively minute quantities will achievethis object in substantial degree. 1 In accordance with our inventionthe objects above mentioned are attained by adding to the moltenaluminum a small amount of beryllium and manganese; I The result of.this addition. is a substantial reduction in the rated formationfof theaforesaid sludge or dress and, in some'ob-I served cases, asubstantially. complete pri'avention of any. dross formation. I Bestresults have been? observedwhere the temperatureof the molten aluminumabsorbingbodyis not much in excess of about 100 .C. above themeltin'gpoint of the aluminum, and we prefer'tomaintain the molten absorbingbody at a temperature within, about 125 C. of its melting point, whichpointwi'll, of: course, vary dependinguponthe amount oimetal' vaporwhich has been. absorbed by the aluminum from the gaseou mixture ofmetal vapor/and carbon monoxide with which it iscontacted. The abovedescribed effect of the presence of the beryllium and mang'aneseflinthemolten aluminum body is observable when the manganese'is present inamounts within the range of, about:0.1 to about 1.0 per cent by weightof the molten absorbing body and the beryllium is present in amountwithin range of about .005 to 0.5 per cent by weight of said body..Thepresence of these elements inselected specific concentrations with:

in these expressed ranges will, insome cases, give.

better results than will other'speci'fic concentrations but usually thebest results haveiap peared when the. beryllium is in the range'of about0.0075 to 0.02 per Centand the manganese is in the range of about 0.2 toabout 0.5-per cent.

Simple. experimentation within the indicated ranges will readilydisclose the best amounts in which these elements may be present 'under'a given set of operating conditions'du'ring theabsorption of the vaporof a metal which ismiscibla with the molten aluminum absorbing'b'ody...

For instance; in vapor from a mixture of magnesium vapor and carbonmonoxide it appears that, in general, the best combination of berylliumand manganese in the molten aluminum absorbing body is that of about .01per cent by weight of beryllium and 0.2 per cent by weight of manganese,but if the absorbent already contains a relatively large amount ofmagnesium, say over about 20 per cent by weight, it may be preferable touse higher amountsof manganese up to 1 per cent. In one instance we haveobserved the presence of 0.01

Per cent by. weight of beryllium and 0.2 per cent by weight of manganeseto practically prevent the abgdrpnbn bf magnesium" all formation ofdross during the absorption of ever, substantial efiects are notproduced-unlessthere are concurrently present both beryllium. andmanganese. The manner in which the mane-.- .ganese functions in themolten' aluminum body is obscure. Analyses of the molten aluminum bodybefore and after contact: with: substantial. amount of carbon monoxideshow that theresi'sz no appreciable change in concentration of. manganese during the period. of contact between the molten aluminum bodyand the gaseous reaction mixture. Hence, weassume that the function ofthe manganese may be that oia negative catalyst. Inany event, however,best results are obtained when. the. manganese and the beryllium areboth present. in the moltenaluminum absorbing body.

The effect. of the beryllium and manganese is, of. course, not limitedto a condition where the molten absorbing body. is entirely composed ofaluminum. In the pr'ocessof the general nature herein described it isoften convenient to use a molten absorbing" body;. a portion of which iscomposed. of the metal the vapor of which is to be absorbed or of ametal different than the metal" vapor which is to be absorbed. However,so long as the molten. aluminum absorbing body principally composed ofaluminum in the sense that it exhibits the characteristics of moltenaluminum to react with carbon monoxide to form the dross in question,the presence of beryllium and manganese in the molten body'will'bebeneficial in reducing or eliminatingthe tendency of. the aluminuminthat' body to react with the'carbon monoxide to form a dross.

The manner inwhi'ch the gaseous mixtures of. metal vapor and carbonmonoxide are contacted with the molten absorbing body forms no part ofthis invention. The. two. classic methods of. achieving this contact.are to pass the gaseous" mixture through the molten absorbing body or topass the. gaseous mixture over the surface of the molten absorbing body.The choice of either of these or other methods of contact are usuallydictatedby' the" practical aspects of the viding said aluminum body witha content of beryllium and manganese, the amount of said beryllium beingabout 0.005 to 0.5 per cent by weight of said body and the amount ofsaid manganese being about 0.1 to 1 per cent by weight of said body.

2.. In a process of metal. recovery in which a gas-vapor mixturecontaining carbon monoxide and a vapor of a metal miscible with moltenaluminum is contacted with a molten aluminum body and vapor of saidmiscible metal absorbed in said body, the improvement consisting inproviding said: aluminum body with a content of beryllium-and.manganese, the amount of said beryllium'beingabout 0.0075 to 0.02 percent by weight of said body and the amount of said manganese-being about0.2 to 0.5 per cent by weight of. said body.

3.11:1. a process of metal recovery in which a gas-vapor mixturecontaining carbon monoxide and a vapor of a metal miscible with. moltenaluminum is contacted with: a molten aluminum body and vapor of saidmiscible metal absorbed in said body, the improvementconsistinginprovidi'ng, saidaluminum body with a content of beryllium, andmanganese, the amount of said beryllium being. about; 0.005 to 0.5 percent by weight of said bod'y'and the amount of said manganese beingabout 0.1 to 1 per cent by weight of said body, and during said processmaintaining said molten body at. a temperature within C. of itsmelting'point.

4. In a process. of recovering magnesium. in which a gas-vapor mixturecontaining carbon monoxide and magnesium vapor is contacted with amolten aluminum body, the improvement consisting in providing saidaluminum body with. a content. of beryllium and manganese, the amount ofsaid beryllium being about 0.005 to 0.5 per cent by weight of said bodyand the amount. of said manganese being about 0.1 m1 per. cent by weightof said body.

5. In a. process of recovering, magnesium in. which a gas-vapor mixturecontaining carbon.

' monoxide and magnesium vapor is contacted with a molten aluminum body,the improvement-consisting in providing said aluminum body with a.content of beryllium and manganese, the amount of said beryllium beingabout 0.0075 to 0.02 per cent by weight of said body and the amount ofsaid manganese being about 0.2 to 015 per cent by weight of said body.

6. In a. process of recovering magnesium in which a gas-vapor mixturecontaining carbon monoxide and magnesiumvapor iscontacted with a moltenaluminum bod'y,., the improvement consisting in providing said aluminumbody with about 0.01 per cent by weight of beryllium and 0.2 per centbyweight of manganese.

- PHILIP 'r. STROUP.

CHARLES B. WILLMORE.

